Blank punching method and apparatus

ABSTRACT

This disclosure relates to a method and apparatus for punching out blanks from sheet materials. The material is laid on a base plate and punch knives are arranged in a pattern upon the material and covered by a pressure plate to form a sandwich assembly which is conveyed through a roller punching machine to force the knives through the material. When the sandwich has passed between two pressure rollers, the pressure plate is returned to its starting position with the aid of one of the rollers which rotate continuously in the same direction. A new sandwich may then be passed between the rollers. In a modification an electromagnetic lifting device is provided comprising a frame on which bar magnets are adjustably mounted so that the punch knives can be removed and replaced without disturbing their original pattern of distribution.

United States Patent 1191 Spengler Apr. 2, 1,974

[54]- BLANK PUNCI-[ING METHOD AND 835,522 11/1906 Higgins 83/284 XAPPARATUS 3,570,340 3/1971 Rohdin 3,301,] 10 l/l967 Stcgncr 83/284 XInventor: Ernst M- p g Lerehenstrasse 2,788,069 4/1957 Noojin, Jr. et al83/50 x 47, D-6056 Hcusenstamm, Germany Primary ExaminerRoy Lake 2Fflcdz g 3 1971 Assistant Examiner-James F. C0811 Attorney, Agent, orFirmW. G. Fassc [21] Appl. No.: 171,520

Related US. Application Data ABSTRACT [63] Continuation-impart of Scr.No. 883,856, Dec. 10, This disclosum relates) a method and apparatus for1969, abandoned. punching out blanks from sheet materials. The matcrialis laid on a base plate and punch knives are ar- [30] ForeignApplication Priority Data ranged in a pattern upon the material andcovered by Dec. 17, 1968 Germany 1815115 a Pressure plate to form aSandwich assembly which is conveyed through a roller punching machine toforce 52 us. c1 83/50, 83/284, 83/532, the knives through the materietWhen the Sendwieh 83/925 CC has passed between two pressure rollers, thepressure 51 Int. Cl 826d 7/06, B26f 1/42 Plate is returned e itsStarting Position w the aid of [58] Field of Search....i 83/29, 39, 50,55, 284, one of the rollers whieh rotate eentihueusly in the 83/531, 532563, 925 CC, 745 same direction. A new sandwich may then be passed 1between the rollers. In a modification an electromag- [56] ReferencesCited netic lifting device is provided comprising a frame on UNITEDSTATES PATENTS, which bar magnets are adjustably mounted so that the Ipunch knives can be removed and replaced without i disturbing theiroriginal pattern of distribution. 3,077,807 2/1963 Wright... 83/532 13Claims, 16 Drawing Figures PAIENIEBAPR 21914 3.800.641

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sum 1our11 PATENTEUAPB 2 am SNEEI '11 0F 11 I O Xmw M hw BLANK PUNCHINGMETHOD AND APPARATUS This is a continuation-in-part application of mycopending application, Ser. No. 883,856, filed Dec. 10, 1969 and nowabandoned. I

BACKGROUND OF THE INVENTION The invention relates to a method andapparatus for punching out blanks or work pieces from sheet or foillikematerials, for example textile fabrics, leather, cardboard, rubber orthe like.

It is known to use punching devices for punching out blanks whereby socalled strip steel knives are used, the knife-edges of which are shapedto match the outline of the work pieces to be punched out. For thispurpose a pressure plate is laid on the punching knives or on the sheetmaterial depending on the arrangement of the knives.

US. Pat. No. 2,168,400 granted to A.J. Evers on Aug. 8, 1939 describes amethod for separating blanks from sheet material by means of cooperatingpressure rollers, as well as upper and lower pressure plates and shapedwires effecting a pressure separation rather than a cutting operation.This known apparatus further requires a reciprocating bed for the lowerpressure plate which may be an integral part of such reciprocating bed.Further a return carriage for the upper pressure plate is required. Theuse of a reciprocating bed requires a reversing motor'which alsoreverses the direction of rotation of the pressure rollers. This is notefficient due to the substantial masses which must be accelerated anddecelerated during each working cycle. US. Pat. No. 3,301,110 granted toH.L. Stegner on Jan. 31,1967 discloses a roller operated punchingapparatus in which a plurality of rollers cooperate to effectuate aprogressive rather than a single impact as in vertical stamping presses.

OBJECTS OF THE INVENTION It is the object of the invention to provide amethod and apparatus suitable for die stamping by means of rollersrotating continuously in the same direction to operate more efficientlythan hitherto.

Another object of the invention is to provide. a die I SUMMARY oF THEINVENTION In a method in accordance with the invention for punching outblanks by means of strip steel knives and a pressure plate, the punchknives are laid on the material and covered by the pressure plate, thepressure plate is returned automatically by the rotation of the punchrollers after the punching and restored to the initial position forcooperation with the next set or stack to be punched.

According to a further feature of the invention, the method may becarried out in such a manner that after the pressure plate has beenremoved after the punching out, the punch knives are locatedelectromagnetically and removed automatically from the material in theform of a positional pattern which is restored to its initial positionand deposited on the material for the next operation, aligned, ifnecessary after being laid down and covered by the pressure plate forthe next punching operation.

According to the invention there is further provided a punchingapparatus wherein a stationary table with conveyor rollers fora punchset or stack is disposed upstream of a roller punching device as viewedin the direction of work flow. A further stationary table is arrangeddownstream of said roller punching device. Supporting rollers forraising and lowering a pressure plate are provided above said stationarytables whereby the pressure-plate can be returned to its startingposition by the rotation of the upper pressure roller.

Furthermore, according to the invention electromagnetic rods may bemovably mounted in a separate, movable frame so that it can be pushed onto the supporting rollers which can be raised and lowered for thepressure plate, instead of the pressure' plate. The punching knives maybe equipped with iron cores, preferably constructed in the form ofejectors for cooperation with the electromagnets.-

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may beclearly understood it will now be described by way of example, withreference to the accompanying drawings, wherein:

FIG. 1 shows in section a view of a set or stack complan view of amodified form of construction of the apparatus according to theinvention;

FIG. 12 shows an end view in the direction of the arrow XII in FIG. 11;

FIG. 13 shows in section a detail on a larger scale;

FIG. 14 illustrates diagrammatically a manner of feeding the set orstack through a gap between two pressure rollers during a punchingoperation;

FIG. 15 illustrates a view similar to FIG. 14 but showing an improvedmanner and device for feeding the set or stack through said gap betweenthe pressure rollers during a punching operation; and

FIG. 16 illustrates a modification of a device according to theinvention employing plan-parallel guide means for supporting the guiderails or rollers.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS strip steel punch knives 2placed on one or more layersof sheet or web material 1 to be cut. Theknives are covered by a pressure plate 4. The material 1 rests on a baseplate 3. These fourparts together form said punch stack P quite similarto a sandwich to which pressure is applied as indicated at 6.

The stack P is assembled on a first stationary table 10 (see FIGS. 2 and3), and passed through a punching device to a second stationary table11. After the punching-out in the punching device 5 the rollers of whichrotate continuously in the same direction, the pressure plate 4 isautomatically lifted from the punch knives 2 and restored to an initialposition on the punch knives for the next operation as will be describedin more detail below. Since FIGS. 2 and 3 are top plan views, the punchknives are not visible.

The return of the pressure plate 4 may be effected as shown in FIG. 2 bypassing it above the punching device 5 or as shown in FIG. 3 by passingit to the side of the punching device 5, as indicated by the dashedarrows.

According to FIGS. 4 to 7, a device suitable for carrying out the methodaccording to the invention comprises a punching device 5 which isillustrated in FIG. 4 as a bridge punch and in FIG. 5 and 6 as apressure roller punch.

The stationary tables 10 and 11 are provided with conveyor rollers 12for supporting the punch stack P. As viewed in the direction of workadvance the table 10 isarranged upstream and the table 11 is arrangeddownstream of the punching device 5. The tables l0, 11 may beconstructed in any desired manner and may be mounted on suitablepedestals 13, 14, for example.

Each table 10 and 11 respectively is provided along its longitudinalsides with supporting rollers 15, which can be raised and lowered, forsupporting the pressure plate 4. The supporting rollers 15 may bemounted in rails 16. The rails 16 with the supporting rollers 15 can beraised and lowered by means of bell-crank levers l7 and linkages 18. Inother words, the rails 16 extending longitudinally adjacent each side ofeach of the tables 10 and 11 can be moved vertically up and down by themeans 17, 18. Each rail is provided with rollers 15 for supporting onlythe edges of the pressure plate 4, so that the rollers 15 associatedwith table 11 can pick up the pressure plate 4 without interfering withthe remainder of the stack P, and the rollers 15 associated with thetable 10 can place the pressure plate 4 on a stack P on this tablewithout disturbing the stack.

In the illustration shown in FIG. 4, the punch stack P is initially onthe table 10 in front of the punching device 5. The punch stack P isthen conveyed through the punching device 5 in the direction of workadvance indicated by the arrow 19.

After the termination of the punching operation, the punch stack P is onthe table 11. In this position, the pressure plate 4 is automaticallylifted from the punch knives 2 by the rails 16 with rollers 15, and isthen in the position shown in FIG. 5. The means for the automaticlifting will be described with reference to FIG. 16.

In the position seen in FIG 5, the pressure plate 4 has been raised tothe top of the upper pressure roller in the punching device 5. At thistime, the rails 16 associated with table 10 have also been raised sothat, by initially urging the pressure plate 4 in the direction of thearrow, as will be described below, the top of the upper pressure rollerwill carry the pressure plate 4 back to the rollers 15 associated withthe table 10, as seen in FIG. 6. The latter rollers may then be loweredon their respective rails to place the pressure plate on a new stack P,i.e., to the position illustrated in FIG. 4. This mode of operationcorresponds to the illustration shown in FIG. 2.

Alternatively, as shown in FIG. 3, the pressure plate 4 may first beconveyed laterally out of the working direction by means of suitablemechanical devices not illustrated,- and brought around the punchingdevice onto the table 10 in front of the punching device.

It is to be particularly noted that in each of these modes of operation,it is not necessary to provide reciprocation for the passing ofmaterials through the punching device, since there is no reciprocatingbed nor any reciprocating pressure plate carrier. Nevertheless the samepressure plate 4 may be employed in each punching operation, and thepressure rollers may be continuously rotating in the same direction. Thefirst above described mode of operation is particularlyadvantageoussince the upper roller is employed to return the pressureplate 4 to its initial position without reversing the rotationaldirection of the upper pressure roller.

In the modes of operation described above the punching knives 2 may beplaced individually on the material 1 on the table 10 or a plurality ofpunch knives 2 may be mounted with very slight spacings between thestrip steel knives, on a common base plate (not shown) and laid on thematerial 1 in this form.

Alternatively, it is possible after lifting the pressure plate 4following punching out as shown in FIG. 5, to locate the punch knives 2electromagnetically and lifting them automatically from the material 1in the form of a positional pattern, and restoring them to the initialposition. The device serving this purpose is illustrated in FIGS. 7 to13.

FIG. 7 illustrates the discharge end of the punching apparatus as shownin the right-hand portion of FIG. 5. In addition, a device M with amagnetic frame 35 is arranged for removing the positional pattern formedby the punching knives 2. The magnetic frame 35 is mounted at a suitableheight on a stand 41. Following a punching operation, instead of beingdirectly returned to the side upstream of the device 5, the pressureplate.4 is pushed onto the magnetic frame 35 by rollers 15. Then themagnetic frame 35, together with the'pressure plate 4 resting thereon,is moved from the device M onto the rollers 15 of the rails 16 as shownin FIG. 8 and lowered onto the punching knives 2.

As illustrated in FIGS. 7 to 13, the frame 35 includes a plurality oftransversely extending electromagnets 32. The ends of the electromagnets32 are provided with rollers 34 (see FIG. 13) which ride in the frame 35to permit adjustment of the electromagnets. As illustrated in FIG. 11,the electromagnets are adapted to be connected to a suitable source ofcurrent to energize the magnets. As is also illustrated in FIG. 11, thepunch knives 2 may be provided with iron cores 33, which cooperate withthe electromagnets so that the knives are automatically attached to theelectromagnets when the frame is positioned on top of the punchingknives and the electromagnets 32 are energized.

After the assembly of the pressure plate 4 and frame 35 is lowered ontothe punching knives 2 as shown in FIG. 8, the current of the source isturned on to energize the electromagnets, and thereby connect thepunching knives to the frame 35.

1 The unit which is formed by this means comprises the punching knives 2located in the form of a positional pattermthe magnetic frame 35 and thepressure plate 4. As in the preceding embodiment of FIG. 3, this unit isbrought to a table at the side of the machine as shown in FIG. 9. Forthis purpose, a portable table as shown in FIG. may be employed. On thetable the pressure plate is first removed from the upper side of themagnetic frame 35 which is then lowered onto an uncut stack of materialbefore the next punching operation. The current is then switched off andthe magnetic frame is raised from the punching knives, thereby leavingthe punching knives on the material. Then the punching knives arealigned (e.g. manually) if necessary and thereafter, the pressure plateis lowered onto the punching knives by means of the devices describedpreviously, whereupon the operation is repeated.

In order to locate and hold the electromagnets in place, hand levers 37,shown in FIGS. 10-13 may be pivotally mounted on frame 35, and biased bymeans of compression springs 36. A pressure shoe 38 extends along thelength of the frame 35 on each side thereof, as shown in FIGS. 11 and13, and the springs 36 urge the levers against the shoes 38 to hold thepressure plate4 against the top of the bar electromagnets. The shoes 38may be manually released by means of levers 37.

The mode of operation with the frame 35 and its electromagnets 32 hasthe advantage of being rather simple since the punch knives may be laidout by hand before the first o'peration, whereupon the punchingoperation can be repeated as often as desired with the same arrangementof punching knives because the positional pattern is maintained andvisible at any time in the open magnetic frame filled only by theelectromagnets 32. Another advantage is the ease with which the patternmay be rearranged or adjusted, if required. Adjustment'is, for example,necessary where the pattern'of a textile material requires a veryprecise alignment 'of the punching knives depending on the course of thethreads of the material. FIG. 14 illustrates on a relatively enlargedscale one arrangement that may be employed for feeding .the stack Pthrough a punching device 5 comprising upper and lower pressure rollersand 51 respectively which, according to the invention are drivencontinuously in the same direction-In FIG. 14 the upper horizontalsurface formed by the conveyor rollers 12 upstream and downstream of thepunching device, is at the same level as the top of the bottom pressureroller 51, that is, the plane of the tops of the rollers 12 extends,tangentially to the top of the pressure roller 51 and perpendicularly tothe plane through the axes of the two pressure rollers 50 and 51. Thearangement of FIG. 14 has been found to be somewhat unsatisfactory incertain operations, especially where about 50 layers of fabric are to becut in one passage through the punching device, since it introducesstresses W in the knives, and may produce travelling waves in thematerial being cut, much in the manner well observed in connection withrolling a sheet of dough with a rolling pin. Such waves are undesirablesince they may cause a shift of the sheets or layers relative to eachother.

It has been found, according to the invention that the above describedproblem may be overcome by employing the feeding arrangement accordingto FIG. 15. In this arrangement, the plane of the top surfaces of therollers 12 is again normal to theplane through the axes of the pressurerollers 50,51 but it is now displaced downwardly toward the axis'of thelower roller 51. Thus, when the stack is first fed into the rollers, theleading edge 55 of the base plate 3 engages the lower roller so that thelower roller lifts the plate 3 from the rollers 12 closest to thepunching device 5, as illustrated in FIG. 15. The figure illustrates thedownward displacement A of the rollers 12, which has been found toprevent buckling of the knives 2 and also to prevent the formation of atravelling wave in the material, as

above described.

The length of the displacement A will be selected in accordance with thethickness of the stack P and the flexibility of the material to be cutas well as with regard to the width of the gap between the rollers 50and 51 and the diameters of the rollers 50 and 51.

In operation of the arrangements of FIGS. 4 to 7, it has been found thatcertain difficulties arise as a result of the use of bell-crank leversl7 and linkages 18 for raising and lowering the rails 16. As can be seenin these figures, the guide rails 16 follow generally accurate paths,and it would be expected that the parallelogram coupling with the use ofthe levers 17 would ensure that the guide rails move in such amannerthat the railslower the pressure plate 4 evenly or rather horizontallyonto the stack P. In practice, however, it has been found that thismanner of raising andlowering the guide rails does not in fact readilypermit the lowering of the pressure plate 4 onto the stack with thedesired parallel relationship between the pressure plate and the stack.I

In order to overcome this problem, as illustrated in FIG. 16, a pair ofvertical guide posts is provided adjacent each guide rail 16, and guidebearings or sleeves 61 are affixed to guide the rails 16 for thevertical movement. The upper ends of the guide posts may be firmly heldagainst movement, for example, by means of interconnecting structuralframe members 62. The arrangement shown in FIG. 16 for guiding the rails16 in their vertical movement is purely illustrative.

In order to raise and lower the guide rails 16, levers 65 may beprovided. The lower ends of these levers are connected to rollers 66which ride inthe slots 67 of horizontally slotted members68 affixed tothe guide rails 16. The levers 65 at each side of the punching deviceare interconnected by a suitable pivoted coupling rod 69, and each leverand rod assembly is operatively' coupled, for example, by way ofhydraulic control members 70, to a central operating control device 71such as hydraulic drive means.

The vertical movement by the means disclosed, for example in FIG. 16 andthe plane-parallel guiding assures proper level lowering of the guiderails. It is to be noted that in the arrangement'of FIG. 16 the guiderails are positioned in the same relationship as in the correspondingFIG. 6, and the guide rails 16 of FIG. 16 are controlled in the samemanner as above described.

As noted above in one embodiment of the invention, the pressure plate 4is returned after a punching operation by raising it and passing it overthe upper pressure roller 50 whereby the horizontal return drive resultsfrom the contact between the upper ridge of the pressure roller 50 andthe pressure plate 4 to effect the movement of the pressure plate. Thisreturn operation may be automatically effected. For example, as furtherillustrated in FIG. 16, a suitable sensor 75 may be employed to detectthe presence of the pressure plate 4, or the rails 16, in such aposition that the pressure plate is ready to be returned. The sensor 75may be any suitable sensor, such as a pressure sensor or a contactswitch. The sensor 75 is coupled to a device 76 suitably mounted to urgethe pressure plate into contact with the top ridge of the upper roller50, so that the roller 50 carries the pressure plate back across the topof the punching device and onto the roller associated with the table 10.For example, the device 76 may be a hydraulic cylinder, or an electricsolenoid, operated in conventional fashion by the sensor 75. The sensor75 and device 76 are mounted by any conventional means for the abovepurpose. I

The raising and lowering is also effected in response to sensing means,such as trip dogs (not shown) which sense the position of the stack.

Although the invention has been described with reference to specificembodiments, it is to be understood that it is intended to cover allmodifications and equivalents within the scope of the appended claims.

What is claimed is: I

1. A method of punching out blanks from sheet material by means ofstrip-steel punch knives and a pressure plate, comprising placing saidmaterial on a base plate,

placing said knives on said material, placing said pressure plate onsaid knives to complete a stack, passing the assembled stack oncethrough a punching device having continuously operating upper and lowerpressure rollers, driving said rollers continuously in the samedirection whereby they rotate in opposite directions relative to eachother, and returning said pressure plate to its initial position byraising said pressure plate and passing it backwards over said upperroller in contact with said upper roller whereby the upper roller movesthe pressure plateback to its starting position to form a secondassembly for a second punching operation in which the same pressureplate is employed in combination with punch knives and a different baseplate and material.

2. The method of claim 1, in which said step of returning said pressureplate comprises raising said pressure plate, inserting magnetic meansbetween said pressure plate and said knives for arranging the knives ina predetermined positional pattern whereby said magnetic means operatesto retain said knives in said pattern, and returning said pressure plateand magnetic means with the knives attached thereto to said initialposition on said different material.

3. An apparatus for punching out blanks from sheet material by means ofstrip-steel punching knives and a pressure plate, comprising a punchingdevice having a feeding input and an output, first conveyor meanslocated upstream of said feeding input as viewed in the direction ofwork flow and second conveyor means located downstream of said outputfor feeding a stack comprised of a base plate, material to be punched,strip-steel punching knives, and a pressure plate through said punchingdevice, said apparatus further comprising first and second carrierroller means movably supported above said first and second conveyormeans respectively for selectively raising and lowering said pressureplate for returning it to its upstream starting position.

4. The apparatus of claim 3, further comprising magnetic holding meansfor holding and transporting said punching knives without changing theirpositions relative to each-other, and means for inserting said magneticholding means between said pressure plate and knives at said secondconveyor means.

5. The apparatus of claim 4, comprising strip-steel punching kniveshaving iron cores for cooperation with said magnetic holding means.

6. The'apparatus of claim 3, wherein said punching device is a rollingmill having an upper pressure roller and a lower pressure roller with agap therebetween for passing said stack through the gap, and driveshafts for continuously driving said rollers in the same directionwhereby the rollers rotate in opposite directions.

7. The apparatus of claim 6, wherein said first conveyor means upstreamof said punching device comprise a plurality of conveyor rollersarranged side by side in a row with parallel axes which are alsoparallel to the axes of said pressure rollers, the top of said conveyorrollers defining a first plane which is displaced downwardly from asecond plane extending horizontally and tangentially to the top of saidlower pressure roller. v

8. The apparatus of claim 7, wherein said first and second planes extendin parallel to each other and normal to the plane defined by the axes ofsaid pressure rollers.

9. The apparatus of claim 6, further comprising means for passing saidpressure plate across the top of said upper pressure roller and incontact therewith from said output to said feeding input.

10. The apparatus of claim 9, wherein said means for passing comprisesmeans. for sensing a pressure plate raised by said second carrier rollermeans to the level of the top of said upper pressure 'roller, and meansresponsive to said sensing means for urging the pressure plate intorolling contact with said upper pressure roller.

11. The apparatus of claim 3, further comprising plane-parallel guidemeans for selectively raising and lowering said first and second carrierroller means.

12. The apparatus of claim 3, comprising a frame, electromagnetic meansin said frame, means at said output for moving a pressure plate fromsaid second carrier roller means onto said electromagnetic means, andmeans for clamping said pressure plate to said electromagnetic means andfor returning said assembled pressure plate and electromagnetic meansonto punch knives at said second conveyor means, whereby saidelectromagnetic means hold said punch knives in determined positionsrelative to each other.

13. The apparatus of claim 12, wherein said electromagnetic meanscomprise elongated electromagnets having rollers at their ends, and atrack in said frame in which said last mentioned rollers are guided,whereby said electromagnets can be selectively positioned in said frame.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N 3 ,8OO,6Il Dated Anril 2. 197

Inventor) Ernst M. Spengler It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

[73] Assignee: Stanztechnik GmbH Roeder & Spengler Bergen-Enkheim ySigned and Scalzd this [SEAL] Attest:

RUTH C. MASON C. IAISIIALL DANN Arresting Officer Commissioner 01bit.and Trademarks thirtieth Day of Deamber 1975

1. A method of punching out blanks from sheet material by means ofstrip-steel punch knives and a pressure plate, comprising placing saidmaterial on a base plate, placing said knives on said material, placingsaid pressure plate on said knives to complete a stack, passing theassembled stack once through a punching device having continuouslyoperating upper and lower pressure rollers, driving said rollerscontinuously in the same direction whereby they rotate in oppositedirections relative to each other, and returning said pressure plate toits initial position by raising said pressure plate and passing itbackwards over said upper roller in contact with said upper rollerwhereby the upper roller moves the pressure plate back to its startingposition to form a second assembly for a second punching operation inwhich the same pressure plate is employed in combination with punchknives and a different base plate and material.
 2. The method of claim1, in which said step of returning saiD pressure plate comprises raisingsaid pressure plate, inserting magnetic means between said pressureplate and said knives for arranging the knives in a predeterminedpositional pattern whereby said magnetic means operates to retain saidknives in said pattern, and returning said pressure plate and magneticmeans with the knives attached thereto to said initial position on saiddifferent material.
 3. An apparatus for punching out blanks from sheetmaterial by means of strip-steel punching knives and a pressure plate,comprising a punching device having a feeding input and an output, firstconveyor means located upstream of said feeding input as viewed in thedirection of work flow and second conveyor means located downstream ofsaid output for feeding a stack comprised of a base plate, material tobe punched, strip-steel punching knives, and a pressure plate throughsaid punching device, said apparatus further comprising first and secondcarrier roller means movably supported above said first and secondconveyor means respectively for selectively raising and lowering saidpressure plate for returning it to its upstream starting position. 4.The apparatus of claim 3, further comprising magnetic holding means forholding and transporting said punching knives without changing theirpositions relative to each other, and means for inserting said magneticholding means between said pressure plate and knives at said secondconveyor means.
 5. The apparatus of claim 4, comprising strip-steelpunching knives having iron cores for cooperation with said magneticholding means.
 6. The apparatus of claim 3, wherein said punching deviceis a rolling mill having an upper pressure roller and a lower pressureroller with a gap therebetween for passing said stack through the gap,and drive shafts for continuously driving said rollers in the samedirection whereby the rollers rotate in opposite directions.
 7. Theapparatus of claim 6, wherein said first conveyor means upstream of saidpunching device comprise a plurality of conveyor rollers arranged sideby side in a row with parallel axes which are also parallel to the axesof said pressure rollers, the top of said conveyor rollers defining afirst plane which is displaced downwardly from a second plane extendinghorizontally and tangentially to the top of said lower pressure roller.8. The apparatus of claim 7, wherein said first and second planes extendin parallel to each other and normal to the plane defined by the axes ofsaid pressure rollers.
 9. The apparatus of claim 6, further comprisingmeans for passing said pressure plate across the top of said upperpressure roller and in contact therewith from said output to saidfeeding input.
 10. The apparatus of claim 9, wherein said means forpassing comprises means for sensing a pressure plate raised by saidsecond carrier roller means to the level of the top of said upperpressure roller, and means responsive to said sensing means for urgingthe pressure plate into rolling contact with said upper pressure roller.11. The apparatus of claim 3, further comprising plano-parallel guidemeans for selectively raising and lowering said first and second carrierroller means.
 12. The apparatus of claim 3, comprising a frame,electromagnetic means in said frame, means at said output for moving apressure plate from said second carrier roller means onto saidelectromagnetic means, and means for clamping said pressure plate tosaid electromagnetic means and for returning said assembled pressureplate and electromagnetic means onto punch knives at said secondconveyor means, whereby said electromagnetic means hold said punchknives in determined positions relative to each other.
 13. The apparatusof claim 12, wherein said electromagnetic means comprise elongatedelectromagnets having rollers at their ends, and a track in said framein which said last mentioned rollers are guided, whereby saidelectromagnets can be selectively positioned in said frame.